Crystal structures of TiO(OH)(2) and Li(2)TiO(3) have been studied in detail and refined using X-ray powder diffraction data. Both compounds possess a high concentration of defects in the structure. The crystal structure of the Li(2)TiO(3) salt obtained at 700 degrees C reveals stacking faults of LiTi(2) metal layers, which leads to the appearance of short-range order in three possible space groups: C2/c, C2/m, P3(1)12. The possibility to stabilise this imperfect state increases the mobility of the Li(+) ions in the structure and allows the complete exchange of lithium by hydrogen in acid water solutions with formation of TiO(OH)(2). The crystal structure of TiO(OH)(2) belongs to the layered double hydroxide structure type with the 3R(1) sequence of oxygen layers and can be described as a stacking of charge-neutral metal oxyhydroxide slabs [(OH)(2)OTi(2)O(OH)(2)]. TiO(OH)(2) is the first layered double hydroxide structure formed by a cation with oxidation state +4 only.
A crystal structure investigation of the low temperature Li 2 SnO 3 modification has been carried out. X-ray, neutron powder and electron diffraction data showed that this compound crystallizes in a monoclinic unit cell with parameters: a = 5.3033(2)Å, b = 9.1738(3)Å, c = 10.0195(2)Å, β~100.042(2)º and has stacking disorder along the c-axis. Simulation of diffraction patterns with different stacking faults mainly reveal the presence of rotational stacking faults with a probability of about 40% .
A comparative analysis of 6,7 Li NMR spectra is performed for the samples of monoclinic lithium titanate obtained at different synthesis temperatures. In the 7 Li NMR spectra three lines are found, which differ in quadrupole splitting frequencies Q Q and according to ab initio EFG calculations are assigned to three crystallographic sites of lithium: Li1 (Q Q a 27 kHz); Li2 (Q Q a 59 kHz); Li3 (Q Q a 6 kHz). The dynamics of lithium ions is studied in a wide temperature range from 300 K to 900 K. It is found that the narrowing of 7 Li NMR spectra as a result of thermally activated diffusion of lithium ions in the low-temperature Li 2 TiO 3 sample is observed at a higher temperature in comparison with a sample of high-temperature lithium titanate. Based on the analysis of 6 Li NMR spectra it is assumed that there is mixed occupancy of lithium and titanium sites in the corresponding layers of the crystal structure of low-temperature lithium titanate, which hinders lithium ion transfer over regular crystallographic sites.
COVER ARTICLETwo new solid MO(OH) 2 (M = Zr, Hf ) oxyhydroxides have been synthesised by an ion-exchange reaction from Li 2 MO 3 (M = Zr, Hf ) precursors obtained by a citrate combustion technique. The crystal structure of the oxyhydroxides has been solved by direct methods and refined using Rietveld full profile fitting based on X-ray powder diffraction data. Both oxyhydroxides crystallize in a P2 1 /c monoclinic unit cell and have a structure resembling that of the related salts. Detailed characterisation of the fine-structure features and chemical bonding in precursors and oxyhydroxide powders has been performed using vibrational spectroscopy, nuclear magnetic resonance spectroscopy, scanning electron microscopy, pair distribution function analysis and quantum-chemical modelling.
Crystal structures of Li2MO3 (M=Sn, Ti) and TiO(OH)2 have been studied in detail and refined using X-ray powder diffraction data. All compounds posses a high concentration of defects in the structure. The crystal structures of the Li2MO3 salts obtained at 700°C reveal stacking faults of LiM2 metal layers, which leads to the appearance of short-range order in three possible space groups: C2/c, C2/m, P3112. The possibility to stabilize this imperfect state increases the mobility of the Li+ ions in the Li2TiO3 structure and allows the complete exchange of lithium by hydrogen in acid water solutions with formation of TiO(OH)2. The crystal structure of TiO(OH)2 belongs to the layered double hydroxide structure type with the 3R1 sequence of oxygen layers and can be described as a stacking of charge-neutral metal oxyhydroxide slabs [(OH)2OTi2O(OH)2].
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